The Japanese online retail giant Rakuten has paid $900m (€660m) for the messaging app Viber as it tries to find new ways to attract customers.

Viber, developed by the Cyprus-based Viber Media, lets smartphone users make free calls and send messages over the internet. The app has more than 300 million registered users and operates in almost 200 countries.

Rakuten, Japan’s largest online retailer, has bought a number of companies in recent years as it looks to move beyond web-based retailing, including the Canadian e-reader maker Kobo and the video on demand service Wuaki.tv.

The Viber acquisition gives Rakuten a foothold in the mobile messaging market, and the company called the purchase a “bold step”.

Rakuten’s chairman and chief executive, Hiroshi Mikitani, called Viber a “total consumer engagement platform”, adding: “Simply put, Viber understands how people actually want to engage and [offers] the only service that truly delivers on all fronts.”

Mobile messaging is seen as a key growth area for e-commerce companies, with many retailers hoping to use the service to reach consumers through their smartphones.

The hugely popular Chinese instant messaging app WeChat is a cornerstone of e‑commerce giant Tencent’s business. Other popular messaging apps include Snapchat, WhatsApp, Line and Facebook Messenger.

Viber’s founder, Talmon Marco, said: “Our vision is to be the world’s number one communications platform and our combination with Rakuten is an important step in that direction.”